Dipolymers of tetrafluoroethylene (TFE) and 3,3,3-trifluoropropene (TFP) show utility in various molded plastic products and in coatings. The major challenge for the preparation of such dipolymers is the absence of any convenient methods that do not require the use of expensive, high pressure reactors, or that do not require organic solvents, which must be recovered and recycled after each use.
Preparation of TFE/TFP polymers is disclosed in U.S. Pat. No. 2,484,530. Pressures of up to 1000 atmospheres are required to produce these polymers. Such high pressures are dangerous on an industrial scale because of the propensity of TFE to deflagrate.
Brown and Wall (Polymer Preprints Amer. Chem. Soc., 1966, 7(2), 1116) prepared several dipolymers of TFE and TFP by using radiation-induced polymerization and a cobalt-60 radiation source. Conversion was under 15%. Use of radioactive material in an industrial process is expensive and impractical due to the requirements of handling the isotope and the extensive shielding needed to protect workers from radiation.
Preparation of TFE/TFP dipolymers in solvents and with a free radical initiator is taught in U.S. Pat. Nos. 5,182,342, 5,286,822, 6,824,930 B1, 6,770,404 B1, U.S. 2004013971 A1, and U.S. 2004038151 A1. When a TFE/TFP dipolymer is prepared in this manner, the solvent must be recovered from the polymerization reactor and the polymer must be extensively dried to remove all traces of solvent.
Therefore it remains a general problem in the field of fluoropolymers to provide a TFE/TFP dipolymer that has high molecular weight and has been produced without the presence of solvents.